Water heaters, of the type adapted to heat water for the purposes of cooking, bathing, washing, and the like, are typically powered either through the use of a gas flame, or through the use of an electric resistance coil immersed within the water. If gas is used to heat the water, a flame is typically provided outside of the water tank, and the water itself is actually heated by convection as the tank itself is heated and dissipates energy into the water. With electric sources on the other hand, an electric coil having a relatively high resistance factor is immersed within the water tank and by providing electric current through the coil, the resistance causes the coil to become heated to a level sufficient to heat the water.
With respect to gas powered water heaters, such devices have typically required a spark to serve as the ignition means to initially ignite the gas which can then be sustained through a continuous supply of gas or fuel thereto. The spark is typically provided through the use of a pair of conductors which are slightly spaced apart, and by providing electric current through one of the conductors, to a sufficiently high level, the current is caused to "arc" across the gap to the second conductor and thereby provide the spark necessary for ignition of the gas. Once the gas is ignited, the current flow through the conductors can be stopped in that the combustion can be sustained through continuously supplying gas.
With respect to electric immersion coils, a relatively high level of electric power is necessary to cause the resistor to become heated to the level necessary for heating the water within the water heater tank. Typically the water heater requires at least a 120 volt AC power source, which is not a difficulty when the water heater is provided within a land-based home which can be connected to the community electrical grid. However, with mobile homes, or recreational vehicles, the ability to provide sufficient power to heat the water tank, is confronted with a new level of difficulty. The twelve volt DC power typically provided on a recreational vehicle is not sufficient to enable the electric resistance coil to be used.
Various means have therefore been provided as a source of power for the hot water heater on board such recreational vehicles. For example, U.S. Pat. No. 5,632,614, assigned to the present assignee, discloses a gas fired appliance in the form of either a furnace or a hot water heater wherein the ignition means for initially igniting the gas is provided in the form of a "hot surface ignition system" wherein the electric power of the recreational vehicle is sufficient to heat a "hot surface", in the form of a resistor, to a level sufficient to ignite the gas, typically propane. Once ignition is reached, current flow to the hot surface can be stopped in that combustion of the gas can be sustained simply by providing a continuous flow of gas to the hot water heater.
Alternatively, the '614 Patent also discloses the use of an electric coil which can be immersed within the water tank and powered by a land-based power source which is able to deliver the 120 volt AC power which is necessary to heat the electric coil sufficient to heat the water.
While the system disclosed in the '614 patent does provide a means by which two different power sources can be used to heat the water within the water heater, it also requires two entirely separate means of sensing and control. For example, with regard to the gas system, a temperature probe is required to be provided within the hot water heater which in turn sends a signal to a processor wherein the processor then compares the actual temperature to the desired temperature, typically entered into the system through a thermostat. Depending on the difference between the actual water temperature and the desired water temperature, the processor can then send a signal to a valve to turn the flow of gas to the gas burner on or off. If in fact the recreational vehicle is parked and has access to a land-based power system, the electrical coil immersion system can be used either instead of, or in conjunction with, the gas burner. However, the electric coil immersion system also requires a temperature probe provided within the hot water heater, and a control mechanism for providing electrical power to the coil.
As a result of these duel systems, the actual control of the water heater can be a rather cumbersome system resulting in an inefficient manner for heating the water within the hot water heater. The user is forced to set and monitor both the gas and the electric power systems. Moreover, the manufacturer of such recreational vehicles, are forced to make expenditures for the dual means of control which necessarily results in a higher cost for the recreational vehicle.